1. Field of the Invention
This invention is directed to tongs, anchor members for tong belt apparatuses, for tongs for rotating an object such as a tubular member and particularly to the field of tongs employing such members and apparatus.
2. Description of the Prior Art
Gripping elements or jaws used in conventional tongs are designed to operate with very high load variations between leading and trailing dies. Jaw guiding slides or linkages are used to control die contact and force delivery. Jaw guides absorb energy and detract from torque delivery. Uneven die loading causes marring or damage to the tubular surface.
In some designs die loading becomes increasingly asymmetrical as pipe size is reduced, substantially increasing die wear and the probability of damage. A power tong should preferably be able to cover a range of pipe sizes without difficulty, and if a further pipe size change is needed, it should be effected with only an interchange of parts. Maintenance and life problems can have an economic significance far in excess of the cost of the dies or even the pipe involved, because the down time that results when replacements or repair must be made involves not only material costs, but also drilling rig and crew costs and the continuing charges for other specialized tools and equipment present at the drilling rig. Thus a power tong system which requires frequent replacement of dies or other elements or which causes undue damage to sections in a pipe string would be far inferior to a power tong system which operates steadily and uniformly.
Both jaw/die tongs and belt/chain tongs can be used with relatively hard and rigid metal tubulars such as casing and tubing. When these tongs are used with thin tubulars or tubulars made from relatively "softer" metals or from premium metals such as high alloy steels or low carbon steels or tubulars made from non-metal materials such as fiber glass, they often literally chew up the tutular.
When working with fiber glass reinforced pipe, serrated or toothed dies (or jaws with such dies) can easily cause marking or damage to tubulars. Such damage results in destruction of reinforcing filaments in the tubular and can considerably reduce the tubular's strength. When the outside surfaces of the fiber glass pipe are irregular or outside diameters of individual joints vary, either inadequate or extreme die penetration is achieved.
U.S. Pat. No. 4,774,860, co-assigned with this application, addressed these problems and taught a new tong which can and has been successfully used with softer tubulars such as fiber glass pipe. The present invention, in one embodiment, teaches an improvement of and simplification of the tongs and apparatuses of U.S. Pat. No. 4,774,860.